Improve Fuzzing for FreeType

Fuzzing is a very important asset when verifying programs, as it reveals critical edge cases that can be missed easily by structured testing.

FreeType is set up to work with OSS-Fuzz already, yet there are many ways to improve it. Apart from making fuzzing faster and more efficient, possible improvements also contain the plan to build a regression test suite in a GitHub repository. Furthermore, this project could be used to separate testing logic from the source code of FreeType by setting up a dedicated testing repository.